Abstract

Introduction: MicroRNA (miRNA) has been shown to play a role in regulating the expression of genes involved in tumor suppression and oncogenesis. High-grade, non-muscle-invasive urothelial carcinoma of the bladder (UCB) harbors a significant risk of progression to muscle invasion. In this study, we sought to identify miRNAs differentially expressed in non-progressive high-grade non-muscle-invasive UCB as compared to pathologically identical lesions that progress to muscle invasion.

Methods: Total RNA was extracted from formalin fixed paraffin-embedded tissue (FFPE) of high-grade non-muscle-invasive (TaG3/T1G3) UCB lesions. Patients were categorized into two groups: non-progressors with at least 3 years follow-up or progressors advancing to ≥T2. Exclusion criteria were previous tumors of the upper tract, prior systemic chemotherapy or previous pelvic irradiation. Total RNA was pooled for microarray analysis from a subset of the non-progressor and progressor groups. Data was analyzed using the LOWESS normalization method. Expression profiles of miRNAs were verified with qRT-PCR on 89 high-grade non-muscle-invasive UCB (68 non-progressors and 21 progressors). Logistic regression analysis was performed to identify miRNAs predictive of tumor progression.

Results: MicroRNA microarray data identified a panel of miRNAs (25) with potential involvement in the progression to invasion of high-grade non-muscle-invasive UCB. 36% of these miRNAs were upregulated and 64% were downregulated in the progressor samples. To validate differential expression of these miRNAs, qRT-PCR was performed on the 89 FFPE tissue samples. Logistic regression analysis of qRT-PCR data revealed decreased expression of miR-203 and miR-205 as predictive of progression (p = 0.031 and p = 0.045, respectively). Subsequent qRT-PCR with miR-203 and miR-205 on 31 muscle-invasive tumor samples (≥T2) showed expression profiles that were similar to those of the non-invasive progressors.

Conclusions: In this study, we have shown that miR-203 and miR-205 can identify patients with non-muscle- invasive UCB at high risk to progress to muscle-invasive disease. Our findings also suggest that such tumors have a biomolecular profile similar to muscle-invasive lesions. Further validation studies are underway to investigate additional miRNAs and determine the mechanism by which these miRNAs promote tumor invasion and progression. These results provide an important tool that can be used to prognosticate the clinical behavior of a very challenging subset of tumors.